Two Synthetic Routes to The Formation of Tungsten Oxide Hybrid Compounds
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Two Synthetic Routes to The Formation of Tungsten Oxide Hybrid Compounds S.V. Chong1, B. Ingham2, and J.L. Tallon1,2 1 Industrial Research Limited, P.O. Box 31 310, Lower Hutt 6009, New Zealand 2 Victoria University of Wellington, P.O. Box 600, Wellington 6005, New Zealand
ABSTRACT
The syntheses of tungsten oxide-organic amine hybrids via homogenous and heterogeneous routes were explored and compared. In the former case, tungstic acid (H2WO4) and an appropriate amine were dissolved in ammonia solution under nitrogen atmosphere, and the product was precipitated out via evaporation of the solvent. In heterogeneous synthesis, a nonaqueous approach was employed in which H2WO4 powder was aged in a solution consisting of the amine dissolved in an appropriate organic solvent. XRD and FTIR showed that the hybrid materials obtained from the two different methods are identical. Based on these findings, we were able to prepare tungsten oxide hybrid films for the first time, by dip-coating tungstic acid films prepared from sol-gel techniques, in a non-aqueous diamine solution. The XRD spectra of these films exhibit a series of harmonic peaks, indexed as [00k], which correspond to the Bragg peaks for the hybrid compounds. SEM shows the morphology of tungstic acid changes from the irregularly shaped platelets to a needle-like structure of the hybrids and resulted in a loosely packed coating.
INTRODUCTION
Self-assembling systems have been a popular topic of investigation in the past few decades due to their relevance to both fundamental and applied sciences. While self-assembled monolayers of silanes, thiols, carboxylates, or sulfides, on surfaces have been more extensively investigated in recent years [1,2], the self-assembling of molecules from solution to form two- or three-dimensional compounds still plays an important part in the development of novel materials. Tungsten oxide has been a much-studied compound due to its rich electronic and structural properties. An example of the former is the amazing colour range displayed in the various tungsten bronze series [3]; while the latter can been seen in the complex arrangement of tungsten oxide octahedra (WO6) through a combination of edge or corner sharing to form 1-, 2-, or 3dimensional network structures [4,5]. Previously, we reported the syntheses of two-dimensional layered hybrid compounds with alternating organic amines and tungsten oxide layers from solution chemistry [6,7]. These hybrids possess plate-like morphology, which resemble that of tungstic acids (WO3·H2O and WO3·2H2O), and their interlayer spacing increases with increasing alkyl chain length of the diamines [6]. In this report, an alternative route to synthesise a few selected W-oxide hybrids is explored. This involved the ageing of tungstic acid powder in a non-aqueous environment, since tungstic acid will dissolve in an alkaline amine aqueous
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solution. In addition, the first preparation of tungsten oxide-amine hybrid films via dip coating will also be presented.
EXPERIMENTAL DETAILS
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